The present invention relates to a device for embossing and laminating continuous plies in order to form a web material.
More specifically, the present invention relates to an embossing and laminating device of the type comprising a pair of embossing cylinders, each of which works in conjunction with a corresponding pressure roller, with a glue applicator which applies glue to at least one of the embossed plies, and with laminating means which join together two plies that have been embossed separately between each embossing cylinder and its corresponding pressure roller.
In the paper converting industry, embossing is often used in the production of toilet paper, kitchen towels, paper serviettes, tissues and similar products in order to modify the paper""s softness and absorbency.
There are various embossing and laminating systems for the production of embossed web materials obtained by joining together two or more plies. In particular, systems exist in which two or more plies of continuous material are embossed separately and then joined together. These systems can basically be subdivided into tip-to-tip laminating systems and nested laminating systems, so-called random nested or xe2x80x9cDERLxe2x80x9d systems or the like.
In the first case (see EP-B-0,370,972), each of the two plies is embossed between an embossing cylinder, which has projections or tips arranged in a repeating pattern, and a pressure roller, which is usually covered in a yielding material such as rubber or the like. The two plies are then joined together by being laminated between the two opposing embossing cylinders which are synchronized so that the tips of one cylinder coincide with the tips of the other cylinder in the lamination nip between the two cylinders, the distance between the cylinders being such as to cause lamination of the plies between the opposing tips. A glue is usually applied to one of the two pliesxe2x80x94to the raised areas produced by the embossing actionxe2x80x94prior to lamination.
With embossing and lamination of the xe2x80x9cnestedxe2x80x9d type, on the other hand, the pliesxe2x80x94which have been embossed separately in a way similar to that described abovexe2x80x94are joined together so that the protrusions of one ply fit between the protrusions of the other ply. In these cases the two embossing cylinders are not pressed against each other in the nip between them and the two plies are joined together by being laminated between one of the two embossing cylinders and a laminating roller. This technique is described in GB-B-1,225,440 and in U.S. Pat. No. 3,694,300.
Italian patent No. 1,213,842 (appl. No. 9519A/87) describes an embossing unit of the tip-to-tip type which has been modified in order to produce a random type nested embossed pattern (xe2x80x9cDERLxe2x80x9d). This is achieved by inserting a diverting element which modifies the path of one of the two plies between the embossing zone and the lamination zone.
Italian utility model application No. 21,325B/89 describes a device that allows both nested type embossing and tip-to-tip type embossing to be carried out by modifying the position of the device members as and when necessary. Basically, in order to switch from one operational mode to the other, the position of the embossing cylinders needs to be altered completely. In practice, what this known technique is in fact suggesting is to convert a conventional tip-to-tip embossing unit into a conventional nested embossing unit each time. This means that very lengthy intervention times are needed in order to change over from one type of embossing to the other. Furthermore, in order to be able to position the laminating roller in this device such that it can work in conjunction with one of the embossing cylinders, it has been necessary to locate the axes of the two embossing cylinders and of the two pressure rollers in one and the same horizontal plane. This brings with it substantial drawbacks on account of the deformations experienced by the embossing cylinders as a result of the high pressures required during embossing, with the effect that there is uneven embossing and lamination between the center and the edges of the plies.
The object of the present invention is to produce an embossing and laminating unit that can operate in both tip-to-tip and nested mode and in which it is easy to switch from one type of embossing to the other, with any operations to set and adjust the device being reduced a minimum.
A further object of the present invention is to produce an embossing unit in which the embossing cylinders and the pressure rollers are positioned so as to reduce any irregularities in the laminated product which occur as a result of bending of the embossing cylinders.
These objects, together with other objects and advantages which will be apparent to those skilled in the art on reading the following text, are achieved using an embossing and laminating device of the type comprising: a pair of embossing cylinders having tips arranged on the two rollers, said two embossing cylinders being positioned with their axes parallel and adjacent to each other so as to form a nip between them; a pair of pressure rollers, each of which works in conjunction with one of the embossing cylinders; a glue applicator associated with one of said embossing cylinders; and a laminating roller positioned downstream of the nip between the embossing cylinders and working in conjunction with the embossing cylinder which is associated with said glue applicator. Essentially, according to the invention, the embossing cylinder associated with the laminating roller has a diameter greater than that of the other embossing cylinder, and said two embossing cylinders have the same peripheral speed and can be synchronized so that the tips of one embossing cylinder coincide with the tips of the other embossing cylinder or, alternatively, the tips of one embossing cylinder fit between the tips of the other embossing cylinder, without changing the distance between the centers of the cylinders. By using two cylinders having different diameters, sufficient space is created to insert a laminating roller downstream of the nip between the embossing cylinders, even when the two pressure rollers are positioned vertically, one above and one below the corresponding embossing cylinders, the axes of which lie in a horizontal plane.
If the space created by using one embossing cylinder with a diameter greater than that of the other is not sufficient to position the laminating roller, provision may advantageously be made to further increase the space available by ensuring that the plane containing the axes of the embossing cylinder with the larger diameter and the corresponding pressure roller is not perpendicular to the plane containing the axes of the two embossing cylinders. This allows one of the two pressure rollers to be distanced from the plane which is tangential to the embossing cylinders and which passes through the nip between them and also makes more space available in which to position the laminating roller, as well as means for cleaning the surface of the cylinder with the larger diameter, said cleaning means being positioned along the periphery of the cylinder, between the laminating roller and the pressure roller. The cleaning means are used to remove glue residues and dust from the embossing cylinder which is associated with the glue applicator.
The angle formed by the two planes can typically be between 90 and 125xc2x0 and preferably between 90 and 105xc2x0.